The present invention generally relates to an apparatus for producing a magnetic tape, and more particularly relates to a device for setting a hub for taking up thereon a magnetic tape which is cut in a predetermined tape width from an original roll of wide magnetic tape.
Recently, magnetic tape has been widely used as a magnetic recording medium in various fields as the performance of magnetic tape has been improved.
Generally, magnetic tape is manufactured by first producing an original roll of tape which is much wider than the rolls of tape to be actually sold. The original roll of magnetic tape is then cut into tapes of a predetermined width in a slitting step. In the slitting step, as shown in FIG. 1, a magnetic tape T.sub.o is cut into a plurality of magnetic tapes T.sub.n with a cutter 20, and the cut tapes are wound at a high speed onto hubs 8, which are provided in a number corresponding to the number of cut tapes. Although not illustrated in FIG. 3, generally, the cut tapes Tn are subjected to further processing such as finishing at the tape edges (cut surfaces), cleaning at the front and rear surfaces, and the like.
Each of the hubs 8 onto which the magnetic tapes T.sub.n are to be wound are removably attached to a boss member 14 of a rotary shaft 7. It is very important, in view of productivity, to make it possible to easily attach/remove the hub 8 onto/from the boss member 14 before the start and after the completion of the slitting step, and it is also very important, in view of maintaining the tape in good condition, to make it possible to surely attach the hub 8 onto the boss member 14 in such a manner that the hub has no play on the boss member. To this end, there have been proposed various devices.
FIG. 2 shows the basic structure of a conventional hub setting device. As shown in FIG. 2, the hub 8 is fitted on the boss member 14 suitably fixed on the rotary shaft 7. Two grooves are circumferentially formed in an outer circumferential surface 16 of the boss member 14, and in the respective grooves, 0-rings 17 made of, for example, NBR (acrylonitrile-butadiene rubber) and coil springs 18 are provided, the 0-rings 17 covering the upper portions of the respective 0-rings 17. The coil springs 18 are arranged so as to suitably project from the outer circumferential surface 16 of the boss member 14.
The hub 8 is inserted onto the thus-arranged boss member 14 in such a manner that an inner circumferential surface 9 of the hub 8 comes into contact with the coil springs 18 and the 0-rings 17 and the coil springs 18 are suitably deformed while being rotated corresponding to the direction of hub insertion (the direction shown by an arrow A) as shown in FIG. 3. The thus-inserted hub 8 is retained due to abutment between the coil springs 18 and the inner circumferential surface 9 (mainly due to the abutment caused by the elasticity of the 0-rings 17).
However, because the 0-rings 17 and the coil springs 18 have considerable variations in diameter and the hub is in line contact (strictly, point contact) with the coil springs 18, the hub cannot be retained securely unless the coil springs 18 are urged against the inner circumferential surface 9 with a considerably large force. However, if this force is too large, the coil springs 18 can easily be worn by the repetitive attachment/removal of the hub. It is therefore difficult to ensure stable retention of the hub over long periods. Further, from a viewpoint of hub insertion, it is desirable to provide a suitable clearance t.sub.1 relative to the groove width l.sub.1 so that each coil spring 18 can be rotated easily, while from a viewpoint of hub retention, the clearance t.sub.1 is not desirable because the clearance allows play of the hub 8 on the boss member, causing deviations in the rotation of the hub, and thereby causing the attitude of the wound tape to be poor or causing microscopic chipping of the hub due to the friction between the inner circumferential surface 9 and the coil springs 18.
If the winding attitude of the magnetic tape T.sub.n wound on the hub 8 is poor, not only is the appearance of the tape not good, but the movement of the tape may be poor in a post-winding step such as a rewinding step in which the magnetic tape T.sub.n is wound onto the reel of a magnetic tape cassette, resulting in undesirable tape condition, for example, damage to the cut edges the tape. There is a further problem that chips of the hub material adhere to the magnetic tape T.sub.n, thus significantly lowering the tape quality.
A variety of boss member structures other than that shown in FIG. 2 have been proposed. However, they are substantially the same as that shown in FIG. 2, and the above problems have not been eliminated yet.